Multiple stage choke control



J. o. sARTo 2, ,229

MULTIPLE STAGE CHOKE CONTROL Aug. 25, 1959 Filed Feb. '5, 1958 2 Sheets-Sheet 1 INVENTOR.

[i W 1- M H ray/ways 1959 J. o. SARTO 2,901,229

MULTIPLE STAGE CHOKE CONTROL Filed Feb. 5, 1958 2 Sheets-Sheet 2 INVENTOR. 077774 0. 3472 0.

Ezr

Unite States Patent MULTIPLE STAGE CHOKE CONTROL Jorma O. Sarto, Orchard Lake, Mich., assignor to Chrysler Corporation, Highland Park, Mich., a corporation of Delaware Application February 5, 1958, Serial No. 713,352 6 Claims. (Cl. 261-39) This invention relates to improvements in automatic means for adjusting the positions of the choke valve for the carburetor of an internal combustion engine at low engine loads and temperatures.

It has been customary heretofore to modulate engine carburetion by means of a bimetallic thermostat coupled with the carburetor choke valve so as to control the latters position at light loads in response to engine temperature. The thermostat is usually arranged to maintain the choke valve partially closed when the engine is at a predetermined comparatively cold temperature. Without some mechanism to the contrary, the thermostat control alone results in too rich a mixture during the usual stages of engine warmup at idling or low load conditions and too lean a mixture as the engine approaches its operating temperature.

It has accordingly been customary to employ a vacuum actuated piston coupled with the choke blade to partially open the latter against the tension of the thermostat so as to achieve a more flexible choke control. In such structures the side wall of the cylinder within which the vacuum actuated piston reciprocates is provided with a port connected with the low pressure portion of the gas intake passage or manifold. The sidewall of the piston is provided with a bypass or vent port adapted to register with the cylinder port when the piston and coupled choke valve move to a predetermined intermediate warmup position. The registering sidewall ports are effective to vent or at least partially vent the low pressure end of the piston to atmosphere and thereby to reduce the vacuum induced force exerted on the piston. In consequence, the piston remains at the intermediate position until the engine temperature rises sufliciently to relax the tension in he thermostatic control, whereupon the remaining vacuum induced force continues to urge opening movement of the choke valve until the engine attains its desired operating temperatures.

Although the choke control devices known to the art heretofore are marked improvements over the thermostatic control alone, such structures are still subject to objection. In order to obtain a suitable lean fuel-air mixture as the engine approaches intermediate stages of warmup, the fuel-air ratio at cold idling conditions is far too lean, with consequent poor engine operation. On the other hand, when the conventional control devices of the type described above are adjusted to obtain the fuel-air mixture enrichment required at cold idling temperatures, the fuel-air mixture at intermediate warmup temperatures is far too rich, with consequent loss of economy.

It has been found that at cold engine temperatures of approximately 30 F. or lower, a comparative constant high fuel-air ratio is required for optimum engine ciliciency. At approximately 30 F, the engine operating characteristics change sharply, so that a progressive decrease in the fuel-air ratio is desired for optimum fuel economy as the engine temperature rises above 30 F. to the desired operating temperature.

It is accordingly an important object of the present 2,901,229 Patented Aug. 25, 1959 invention to provide an improved device for controlling a carburetor choke valve, thereby to modulate the fuel-air ratio at idling or low engine loads so as to obtain an idle fuel enrichment at comparatively cold temperatures which closely approximate optimum engine requirements and yet obtains optimum fuel economy at intermediate conditions of engine warmup.

Another object is to provide such a device which is comparatively simple and inexpensive in construction, highly efficient in operation, and capable of rendering comparatively standardized carburetor idling characteristics when produced by mass production methods.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

Figure 1 is substantially a fragmentary side elevational view showing portions of a choke control device embodying the present invention.

Figure 2 is substantially a fragmentary plan view of the structure of Figure 1.

Figure 3 is a fragmentary transverse sectional view of an internal combustion engine employing the present invention.

Figure 4 is a fragmentary enlarged sectional view showing the vacuum actuated choke control piston at the cold starting position.

Figure 5 is a view similar to Figure 4, showing the vacuum actuated piston at a later stage of engine warmup.

Figure 6 is a diagrammatic representation of the choke blade angle with respect to intake manifold temperature.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways.

Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Referring to the drawings, a carburetor 10 is illustrated in Figure I mounted on the customary inlet riser 11 of a piston-type internal combustion engine 12 having a number of driving pistons 13 reciprocable in corresponding engine cylinders 14. The carburetor 10 comprises an air horn casting 15 which contains the customary unbalanced pivotal choke blade or valve 16, an intermediate body casting 17 which includes the fuel bowl 18, and a lower throttle body casting 19 containing the customary throttle valve 20. An intake air passage 21 extends vertically within the carburetor from an upper air filter, not shown, through the air born 15, the intermediate casting 17, and throttle body 19 and communicates at its lower end with the intake passage 22 in the riser 11 to which the carburetor 10 is suitably secured. Upper and lower idle fuel supply ports 23 and 24 respectively, open into the throttle body portion of passage 21 to supply fuel :for engine idle or low load operation.

Intake passage 22 extends to the engine cylinder 14 to supply the latter with a combustible air-fuel mixture as determined by engine requirements in accordance with operation of the inlet and exhaust valves 25 and 26 respectively. The passage 22 is one of several branch passages including passage 22a of the engine intake manifold, which lead to the various engine cylinders 14. Accordingly the intake manifold temperature, which in turn is responsive to engine temperature, is a measure of the temperature of the combustile fuel-air mixture conducted to the engine. The combustion products are exhausted via exhaust manifold 27. The structure thus far may be conventional and is accordingly not described in further detail.

Referring to Figure 1, when the engine is cold and is not operating, choke valve 16 is normally maintained in a closed position by a coiled" bimetallic thermostatic spring 28, rFigurew4, secured at opposite ends to shaft 29of choke-valve 16 and to'a fixed portion 30 of the air horn '1'5. The thermostatic spring 28-is responsive to changes in the temperatureof tlie'intake passage or'rnanifol'd -2122 and progressively relaxesits tension'urgmg valve .16 to the closed position as the intake manifold temperature rises. Spring 28 is illustrated somewhat schematically in the drawings, inasmuch as other preferred couplings between'the spring 28 and valve 15 and other preferred locations of the spring 28 to-render the same most responsive to intake manifold temperature are well known to the 'art.

:Inorder to supplement operation of the thermostatic spring 28in modulating the position of the choke valve when-the engine is'idling oroperating at light loads, a cylinder 31 is-provided as an integral casting with the air horn 15. The left hand or outer end of cylinder 31 isclosed by a plate 32, whereas the inner or right end opens through a ventopening 33 into the air horn portion of inlet passage 21 at a location above or upstream of the choke valve 16 when the latter is closed, Figure 1. A hollow piston 34 closed at its leftend and opening at it'sright end into the 'vent portion of cylinder 3'1 is pivotally secured by a transverse pin 35 to the outer and lower end of a dog-leg lever 36. The upper end of lever 36 is pivotally connected by a pin 37 to the upper end of a shorter arm 38 whichextends perpendicularly to the choke blade 16 and is secured to the smaller or upper extension thereof adjacent the shaft 29. The length of the arm 38 is'approximately one-half the distance between the pivots 35 and 37 so as to afford adequate leverage for'rocking valve 16 as described below. Also'as is apparent from Figure 2, the axes of cylinder 31, lever 36,-and arm 38 are on the transverse verticalmidplane through valve 16 was to achieve a symmetrical arrangement of the linkage connecting piston 34 and valve 16 and to minimize the possibility of jamming or'cocking of the linkage or piston 34;. This latter feature is important in order to minimize friction in a structure of the type shown because the forces operating on the valve 16 are small.

Extending longitudinally from the inner or vent end of piston 34 is a radially opening vent groove 39 of gradually decreasing depthwhich communicates at its inner end with vent opening 33 via cylinder 31.

Extending longitudinally within the inner side wall of the outer endofcylinder 31 is a recess 40 in communication with a conduit 41 which extends through the body of the carburetor and opens into the inlet passage 21 at a location in the throttle body 19 below or downstream of the throttle valve 20 when the latter is closed, Figure 1. Within the side wall of the cylinder 31, the upper end of conduit 41 is restricted at 42, whereby a controlled low pressureis induced within the leftward or outer end of cylinder 31 when the engine .12 is operating at an idling or low load condition. Th piston 34 is dim'en- During operation of the engine at idling or low load con ditions, a comparatively low pressure is developed in the portions of the intake passag 2122 downstream of the throttle valve-20, which lowpressure istransmittedvia conduit 41 and restriction 42 to the low pressure end of cylinder 31. The tapered duct 39'is dimensioned at its smaller end with respect to the cross sectional area of 4- cylinder 31 and the tension of spring 28 to cause shift ing of piston 34 immediately to the position shown in Figure 4 when the intake manifold temperature is between approximately 30 F. and minus 20 F., thereby to open choke valve 16 to a cold idling position which assures a high constant idle fuel enrichment.

The desired position of angular adjustment of choke valve 1691 the cold 'idling position is substantially independent of temperature changes below 30 F., but depends upon the operating characteristics of the carburetor and engine. Thus the cold idling position of the choke valve blade may range from approximately 15 to 30 of arc, depending upon the engine and carburetor design. For any given carburetor and enginedesign, the preferred cold idling position remains substantially constant at normally encountered temperatures below approximately 30 F. It is therefore important to dimension restriction 42 and the smaller end of duct 39 sothat when piston 34 shifts to'the' cold idling position of Figure4,'sufiici ent air will be vented via openings 33, '39, and 40 mm the outer low pressure end of cylinder 31to prevent further leftward'rnovement of'piston 34'until the engine temperature warms to approximately 30 F. This first stage of operation of piston 34' is indicated at I, Figure 4, whereat duct39is'in communication with recess'40. Thus during idling of the engine at all normally encountered temperatures below approximately 30 F. down to approximately minus 20 F., choke valve 16 will be shift ed to the cold idling position I, which in the present instance'is indicated at 30 of are.

It is well known that at intake' 'manifold temperatures above approximately 30 F. a sharp'change takes place the engine idling characteristics and the required minimum fuel-air ratio for idling or low load operation progressively decreases with increasing'temperature. Accordingly the temperature-tension response of spring 28 is determined with respect toth increasing cross sectional area of the tapered duct 39, the restriction 42, and the cross sectional area of piston 34, so that when the intake manifold temperature progressivelyrises above 30 F., the tension of thermostatic spring 28 will gradually relax and enable progressive leftward movement of the vacuum actuated piston 34 to adjacent the final stage of warmup II of Figure 5. As piston 34 moves leftward from the cold idling position, the area of communication between duct 39 and recess 40 increases, thereby to increase the vent action and to decrease the vacuum force urging piston 34 to the left. The resultant of the spring force of thermostatic spring 28 and the vacuum force urging piston 34 leftward are suitably predetermined so that as the manifold temperature rises to a secondary condition of warmup, S, the choke valve 16 will progressively open to maintain the desired fuel-air ratio for optimum fuel economy and operating efficiency.

During the stage of the operation between positions I and II, the choke angle gradually increases along the curve shown in Figure 6 as theintake manifold temperature rises from the cold idling temperature C of approximately 30 F. to th secondary intermediate idling temperature S of approximately to F.

Thereafter as piston 34 shifts leftward in the region of position II of Figure 6 to the fully open position, the maximum vent action through duct 39 and recess 40 is obtained and the vacuum force urging piston 34 leftward rapidly diminishes, as does also the tension in thermostatic spring 28. The choke valve 16 then progressively moves to its fully open position primarily in accordance with the forces resulting from downwardly of economical manufacture by mass production methods, as for example, by a screw machine, process, yet the resulting operation of the conical piston will be substantially the same as described above in reference to the tapered duct 39.

I claim:

1. In a device for regulating the choke valve position for the carburetor of an internal combustion engine at conditions of low engine load and temperature, the combination of a gas intake passage connecting said carburetor with said engine, means responsive to the tem perature of said intake passage for yieldingly regulating the position of said choke valve, a throttle valve in said passage, a cylinder having one end in communication with said passage upstream of said throttle valve, 3. piston reciprocable in said cylinder, means connecting said piston and choke valve for progressively opening the latter upon movement of said piston in one direction away from said one end, a radially opening air bleed duct in the side wall of said piston communicating with said one end, conduit means connecting said cylinder with said passage downstream of said throttle valve, said conduit means opening at the sidewall of said cylinder at locations in communication with said bleed duct when said piston is in a range of positions extending in said direction from a cold idling position, said bleed duct having a progressively decreasing cross sectional area in said direction to progressively increase it area of communication with said conduit means upon progressive movement of said piston in said one direction from said cold idling position.

2. In a device for regulating the choke valve position for the carburetor of an internal combustion engine at conditions of low engine load and temperature, the combination of a gas intake passage connecting said carburetor with said engine, means responsive to the temperature of said intake passage for yieldingly regulating the position of said choke valve, a throttle valve in said passage, a cylinder having one end in communication with said passage upstream of said throttle valve, a piston reciprocable in said cylinder, means connecting said piston and choke valve for progressively opening the latter upon movement of said piston in one direction away from said one end, a radially opening air bleed duct in the side wall of said piston communicating with said one end, restricted conduit means connecting said cylinder with said passage downstream of said throttle valve, said conduit means opening at the sidewall of said cylinder at locations in communication with said bleed duct when said piston is in a range of positions extending in said direction from a cold idling position, said bleed duct decreasing in said direction to progressively increase its area of communication with said conduit means upon progressive movement of said piston in said one direction from said cold idling position, said piston and the small end of said bleed duct being dimensioned in accordance with said temperature responsive means to hold said piston substantially at said cold idling position in opposition to the position-regulating force of said temperature responsive means during idling of said engine when said intake passage is at temperatures below a predetermined cold idling temperature.

3. In a device for regulating the choke valve position for the carburetor of an internal combustion engine at conditions of low engine load and temperature, the combination of a gas intake passage connecting said carburetor with said engine, means responsive to the temperature of said intake passage for yieldingly regulating the position of said choke valve, a throttle valve in said passage, a cylinder having one end in communication with said passage upstream of said throttle valve, a piston reciprocable in said cylinder, means connecting said piston and choke valve for progressively opening the latter upon movement of said piston in one direction away from said one end, a radially opening air bleed duct in the side wall of said piston communicating with said one end,

conduit means connecting said cylinder with said passage downstream of said throttle valve, said conduit means opening at the sidewall of said cylinder at locations in communication with said bleed duct when said piston is in a range of positions extending in said direction from a cold idling position, said bleed duct decreasing in said direction to progressivelyincrease its area. of communication with said conduit means upon progressive movement of said piston in said one direction from said cold idling position, said piston and the small end of said bleed duct being dimensioned in accordance with said temperature responsive means to hold said piston substantially at said cold idling position in opposition to the position-regulating force of said temperature responsive means during idling of said engine when said intake passage is at temperatures below a predetermined cold idling temperature, said bleed duct enlarging toward said one end in accordance with the temperature-tension response of said temperature responsive means to effect a substantially predetermined progressive movement of said piston in said one direction upon a predetermined progressively rising temperature of said intake passage.

4. In a device for regulating the choke valve position for the carburetor of an internal combustion engine at conditions of low engine load and temperature, the combination of a gas intake passage connecting said carburetor with said engine, means responsive to the temperature of said intake passage for yieldingly regulating the position of said choke valve, a cylinder, a piston reciprocable in said cylinder, means connecting said piston and choke valve for progressively opening the latter upon movement of said piston in one direction, vent means, said piston having a generally conically tapered portion of increasing diameter in said one direction, thereby to provide a bleed duct of decreasing area in said direction between the juxtaposed sidewalls of said piston and cylinder, the large end of said bleed duct being in communication with said vent means, conduit means connecting said cylinder with a low pressure region of said passage, said conduit means opening at the side wall of said cylinder at 1ocations in communication with said bleed duct when said piston is in a range of positions extending in said direction from a cold idling position.

5. In a device for regulating the choke valve position for the carburetor of an internal combustion engine at conditions of low engine load and temperature, the combination of a gas intake passage connecting said carburetor with said engine, means responsive to the temperature of said intake passage for yieldingly regulating the position of said choke valve, a cylinder, a piston reciprocable in said cylinder, means connecting said piston and choke valve for progressively opening the latter upon movement of said piston in one direction, vent means, said piston having a portion of increasing diameter in said one direction, thereby to provide a bleed duct of decreasing area in said direction between the juxtaposed sidewalls of said piston and cylinder, the large end of said bleed duct being in communication With said vent means, conduit means connecting said cylinder with a low pressure region of said passage, said conduit means opening at the side wall of said cylinder at locations in advance of said piston in said direction and also in communication with said bleed duct when said piston is in a range of positions extending in said direction from a cold idling position.

6. In a device for regulating the choke valve position for the carburetor of an internal combustion engine at conditions of low engine load and temperature, the combination of a gas intake passage connecting said carburetor with said engine, means responsive to the temperature of said intake passage for yieldingly regulating the position of said choke valve, a cylinder, a piston reciprocable in said cylinder, means connecting said piston and choke valve for progressively opening the latter upon movement of said piston in one direction, vent means, a bleed duct in communication with said vent means and eigteriding'fbtween thifixta iosed' sidewalls of said bylinder and piston, CO'Iidliit m'ean's conncting" saidcylinder with a1o,w{p-i'essur' 'r'egiowof" said "passage; said conduit means opfiingat tHe sidwall -of said 'cyli ndr at locations inadVancebf said piston 'in' said dirctiomand also in communication with said bleed duct-wh'en-said piston is in 'a range of positions extnding' in said direction from a cold idling-position; the cross sectional area'ofsaid bleed duct progressively increasing lengthwise-thereof to References Cited in the file of this'patent 

